The present invention relates to a method and apparatus for positioning workpieces in surfacing machinery, and in particular, an automatic centering system for automatically centering workpieces in a finishing machine, specifically an automatically centering system for a sectional shoe assembly or an infeed assembly, having opposing shoes or feed rollers connected via hydraulic balancing circuits. The hydraulic balancing circuits are coupled by a valve which selectively separates or connects the circuits, allowing the opposing shoes or rollers to selectively move together or independently, respectively. When the circuits are connected by opening the valve, the centerline location can be adjusted.
Surfacing machinery is used to perform surface operations on workpieces, for example, to sand or plane lumber, planks, panels, etc. Such surfacing machinery typically includes upper and lower heads for cutting or sanding the workpieces, and a feed assembly for advancing the workpiece through the heads. The feed assembly preferably provides a self-centering effect so that whatever amount of material is being removed, one-half will be removed from each side, thereby maximizing yield.
Self-centering feed assemblies for abrasive grinding machines are disclosed in U.S. Pat. No. 4,322,919 issued to Gerber on Apr. 6, 1982 and in U.S. Pat. No. 4,640,056 issued to Stump on Feb. 3, 1987, both of which are herein incorporated by reference. These prior art feed assemblies allowed each workpiece to float or center at the sanding head position and to thereby achieve equal stock removal on each side of each board. Because the abrasive belt heads themselves had a self-centering effect, these feed assemblies were required to provide the necessary horizontal forces required to feed each board, but follow the surface of each board so as to not interfere with the centering effect at the abrasive belt heads.
However, when used in connection with cutting heads, as opposed to sanding or grinding heads, these prior art feed assemblies were not adequate to achieve the desired individual centering result, since the cutting heads do not provide a self-centering effect. This is due to the fact that when using cutting heads instead of abrasive heads, the vertical forces on the workpiece are exactly the opposite, as a cutting head tries to pull the board into the cutter, whereas an abrasive head tries to push the board away from the abrasive belt. As a result, the cutting heads would remove an unequal amount from each side and tend to gouge or otherwise cut the workpiece unevenly, especially if the workpiece is uneven, warped or contains other variations. In an attempt to compensate for such problems, the cutting heads normally are displaced relative to each other, as opposed to the desired position of directly opposing each other, resulting in uneven stock removal from each side.
Accordingly, there is a need in a cutting head planer machine for a method and apparatus to adequately center and feed workpieces to the cutting head assembly so that an equal amount of material will be removed from both sides of each and every board independent of individual board thickness variations. There is a further need in all types of surfacing or finishing machines to provide an improved centering assembly. The present invention fulfills such needs.
The present invention comprises an automatic centering system for a sectional shoe assembly or an infeed assembly for use in surfacing machinery. The shoe assembly and the infeed assembly include a plurality of individually movable biasing element sets, i.e., shoe sets and feed roller sets respectively, each set comprising an upper element and a lower element. Each element set is operatively connected to a closed circuit, double rod end hydraulic cylinder assembly which selectively and independently positions the element set responsive to the surface to the workpiece. A means for exerting a force is provided to selectively position each element set to provide a centering force. The means for exerting a force can take the form of an air circuit which selectively exerts pressure on the double rod end hydraulic cylinders of the centering assembly.
The hydraulic cylinder assembly includes two circuits coupled by a valve. When the valve is closed, the circuits are separated and the element sets move together. When the valve is open, the circuits are joined and the element sets move independently of each other.
In use, when the valve is closed, as the upper or lower element of an element set is forced away from the centerline of the workpiece, the opposing element will automatically move the same amount. The shoe and/or infeed assembly thus centers each and every workpiece independent of the amount of stock removal required. When the valve is open, the upper or lower element of an element set is free to move independently of the other element. As such, the centerline position can be easily adjusted.
Accordingly, it is the principle object of the present invention to provide a method and apparatus for positioning workpieces in surfacing machinery.
It is a further object of the invention to provide a centering assembly for centering workpieces in a surfacing machine.
It is also an object of the invention to provide an automatic centering assembly that adjusts for individual workpiece thicknesses and widths allowing multiple workpieces to be centered and planed at the same time by a surfacing machine.
It is an additional object of the present invention to provide a hydraulic cylinder assembly for a shoe or infeed assembly.
It is another object of the present invention to provide an improved centering assembly having a closed circuit, double rod end hydraulic cylinder assembly.
It is yet another object of the present invention to provide in a centering assembly, a hydraulic cylinder assembly including two circuits coupled by a valve to provide selective movement of element sets of the centering assembly.
Numerous other advantages and features of the invention will become readily apparent from the detailed description of the preferred embodiment of the invention, from the claims, and from the accompanying drawings in which like numerals are employed to designate like parts throughout the same.